Pollution of delivery ward air by nitrous oxide. Effects of various modes of room ventilation, excess and close scavenging.

According to a survey to all Swedish delivery departments, nitrous-oxide-oxygen analgesia given on demand is frequently used by women in labour. Excess gas scavenging equipment was lacking in 12 out of a total of 73 delivery wards in September 1982. The effects of various room ventilation and excess gas scavenging methods on the nitrous oxide concentration in the delivery room were investigated. The 8 h time weighted average (TWA) for midwives was 24 ppm nitrous oxide with room ventilation in accordance with the Swedish recommended standard and with excess gas scavenging using 1.61 reservoir tube volume. For women in labour, close scavenging using various modifications of conventional tube systems was shown to be practically impossible to apply. Close scavenging via a specially designed plastic hood surrounding the face of the woman in labour resulted in very low nitrous oxide concentrations in the delivery room, even when the room ventilation was reduced to very low values.